Process for preparing a pharmaceutical formulation of contrast agents

ABSTRACT

The invention relates to a process for preparing a liquid pharmaceutical formulation containing a complex of macrocyclic chelate with a lanthanide and a mol/mol amount offree macrocyclic chelate of between 0.002% and 0.4%, advantageously between 0.02% and 0.3% and very advantageously between 0.025% and 0.25%, the macrocyclic chelate advantageously being chosen from DOTA, NOTA, DOTAGA, DO3A, BT-DO3A, HP-DO3A and PCTA, and is preferably DOTA, the said process comprising the following successive steps: b) preparation of a liquid pharmaceutical composition containing, firstly, the complex of macrocyclic chelate with a lanthanide, and, secondly, free macrocyclic chelate and/or free lanthanide; c) measurement in the pharmaceutical formulation obtained in step b) of the concentration of free macrocyclic chelate C ch1  and/or of free lanthanide C lan1 ; d) adjustment of C ch1  and/or of C lan1  so as to obtain C ch1 =C t ch1  and C lan1 =0, wherein c t ch1  is the target concentration of free macrocyclic chelate in the final liquid pharmaceutical formulation.

The invention relates to pharmaceutical formulations of contrast agents,in particular of complexes of chelates with paramagnetic metal ions,especially for magnetic resonance imaging, and to industrially efficientprocesses for obtaining these formulations.

Many contrast agents based on complexes of chelates with lanthanides(paramagnetic metal), in particular with gadolinium, are known, and aredescribed, for example, in document U.S. Pat. No. 4,647,447. Severalproducts are marketed, especially based on macrocyclic chelates such asDOTA gadoterate (1,4,7,10-tetraazacyclo-dodecane-N,N′,N″,N″′-tetraaceticacid) and gadoteridol HPDO3A, and linear chelates such as DTPA(diethylenetriaminepentaacetic acid) and DTPA-BMA (gadodiamide).

In the body, the complexes of chelates with lanthanide are in asituation of chemical equilibrium, which may lead to a risk of undesiredrelease of the lanthanide, and more especially of gadolinium. A personskilled in the art is thus led to seek technical solutions that limitthis risk in order to solve the complex problem of tolerance in thepatient as safely as possible. This problem is all the more difficultsince the administration of contrast agents is often repeated duringdiagnostic examinations and/or for the guiding and monitoring of theefficacy of a therapeutic treatment.

Several approaches for improving the tolerance of complexes of chelateswith gadolinium are described in the prior art.

More than twenty years ago (U.S. Pat. No. 5,876,695), those skilled inthe art were working on formulations consisting of the addition to alanthanide-complexing chelate of an amount of chelate in excess, i.e.chelate non-complexed by the lanthanide. This excess chelate is intendedto compensate for an undesired release of lanthanide, the excess chelatethen complexing with the released lanthanide (Gd³⁺ metal ion).

In U.S. Pat. No. 5,876,695 the chelates (ligands L) added in excess formacrocyclic chelates are described under the form of an excipient havingthe formula X[X′,L], where X and X′ are metal ions (especially calcium,sodium, zinc or magnesium) and L is the chelate in excess. Theseexcipients are designed to scavenge free lanthanide.

For instance for the chelate DOTA, an excipient is Na2[Ca-DOTA]: theDOTA chelate in excess is complexed by the calcium ion Ca2+ in the cageformed by the chelate, with a resulting charge 2+ to be neutralised bytwo Na+ ions.

A few years later, an improvement of these excipients X[X′,L] waspresented in the patent EP 454 078 (U.S. Pat. No. 7,385,041) withimproved X[X′,L] where both X and X′ are calcium or zinc, theseexcipients being able even at low dosage (0,1% mol/mol) to scavenge bothfree lanthanide and free organic ligand chelate. This document coversthese excipients, in particular for example the calcium salts of calciumchelated complex, notably Ca[Ca-HPDO3A]₂ instead of Na[Ca-HPDO3A], andexplains (in detail notably column 1 lines 21-40) that a freemacrocyclic ligand L instead of such excipient X[X′,L] should not beused for safety reasons due to the toxicity of free chelate L. Inparticular, table 1 of U.S. Pat. No. 7,385,041 illustrates with LD50values that free macrocyclics chelates (HP-DO3A, DO3A, DOTA) are aboutat least 10 times more toxic than these macrocycles under the formX[X′,L]. In particular for DOTA, the LD50 is at least about 40 timesbetter for Na2[Ca-DOTA] than for free DOTA.

Chelate Letal dose (LD 50) mMol/Kg Free macrocyclic HP-DO3A 0.11 chelateL (not used DO3A 0.12 as excess ligand) DOTA 0.18 Excipient X[X′,L]Ca[Ca-HPDO3A]₂ 1.3 Ca[Ca-DO3A]₂. 1.6 Na2 [Ca-DOTA] >7 Chelate-Gd DOTA-Gd14 HP-DO3A-Gd 12

The formulation of the commercialised product gadoteridol (ProhanceBracco) includes 0.1% Ca[Ca-HPDO3A]₂, and gadobutrol product (GadovistBayer Schering) includes Na[Ca-BT DO3A] excipient.

As a conclusion, no document of the prior art describes that theformulation of a macrocyclic chelate administered to the patientcontains or should contain, besides the macrocyclic chelate complexed bythe lanthanide, an excess of free macrocyclic chelate (in a specific andlow range) that is under the form of a free chelate L which was notcomplexed with any metal ions and in particular that is not under theform of an excipient X[X′,L]. On the opposite the one skilled in the artwas discouraged to do so due to a risk in terms of tolerance of freemacrocyclic chelate.

It is also emphasized that in the prior art for the macrocyclic chelate(contrarily to the invention as described later), the dedicatedexcipient X[X′,L] was added after the complexation of the chelate by thelanthanide (see the numerous examples of U.S. Pat. No. 5,876,695 andU.S. Pat. No. 7,385,041). The complexation was realised according to thesteochiometric proportions of the chelate L (HP-DO3A for example) andlanthanide “Ian” (Gd3+ for example). Following scheme I describes themanufacturing process of the prior art (sp means stoechiometricproportions):

PRIOR ART Macrocyclic Chelates

use of free macrocyclic exipient unwanted

Despite all these prior-art studies, the complex problem of tolerancestill exists, especially in situations at risk of more pronouncedtolerance for the administration of MRI contrast products. For instancea very different approach was tested recently as illustrated in WO2007/106 544 with grafting onto the chelates chemical groups intended toincrease the affinity of the chelate for the metal.

A new problem has moreover recently appeared in the matter of tolerance,namely a pathology known as NSF (nephrologic systemic fibrosis, orfibrogenic dermopathy, with very severe effects on human skin), whichmay be at least partly correlated to the existence of free gadolinium,i.e. non-complexed gadolinium, in the body. This disease has led tohealth authorities being alerted as regards certain categories ofpatients with respect to marketed gadolinium-based contrast agents.Briefly, NSF could be associated to the transmetallation of somelanthanide from the complex [lanthanide-chelate] by endogenic ions suchas zinc and resulting in unwanted release of free lanthanide.

In summary, this problem of tolerance of complexes of chelates withlanthanides remains complex and important, leading to the research ofeven more safe products, and to the necessity of a perfectly controlledrate of the different entities in the pharmaceutical solutions.

The Applicant has worked on the specific case of macrocyclic chelates,and has demonstrated, contrary to what was expected, the very satisfyingtolerance obtained when using an amount of excess free macrocyclicchelate at a particular low dose range, and not under the form of anexcipient X[X′,L] of the prior art.

The Applicant has shown that with macrocyclic chelates, and inparticular DOTA, results are very advantageous, using a very low excessof free chelate L, so that the pharmaceutical composition administeredto the patient contains more specifically between 0.02% and 0.4% and inparticular between 0.025% and 0.25% of the free macrocyclic chelate L.

For the purposes of the present invention hereafter, the term “freemacrocyclic chelate” means any macrocyclic chelate L not complexed withlanthanide or with other metal ions, and in particular not under theform of an excipient X[X′,L] in which X and X′ are as described above.

Briefly the formulation selected by the Applicant with free macrocyclehas the strong advantage, notably in view of the NSF, of increasinghighly the scavenging capacity of potential free gadolinium, as comparedto the prior excipients X[X′,L], as explained further in detail in theapplication.

Consequently, in view of this low amount of free excess, a new problemarises, which is unknown in the prior art, namely the need for extremelyprecise and delicate industrial-scale control of the concentrations offree macrocyclic chelate and thus of the manufacture of the product toarrive at this range of target values of amount of free chelate, thesevalues needing to be stable, including after storage for several monthsor years.

Specifically, taking into account the production volumes, which are ofthe order of several tens of tons of active principle, the Applicant hadto develop a new and particularly optimised preparation process thatmakes it possible to ensure the reliability and reproducibility of thecomposition of commercialized batches.

In particular, the Applicant found that the mixing of stoichiometricamounts on the basis of the theoretical calculation does notsufficiently satisfactorily give at the industrial scale the respectiveamounts of complex of chelate with the lanthanide and of free chelate inlow concentration in the pharmaceutical formulation. The reason for thisis that it is then necessary to perform several analysis steps, whichtakes several hours, and significantly increases the industrial costprice of the product. In contrast, the Applicant's process makes itpossible especially to prepare beforehand and to optimize the analyticaldevice, which is important as regards its impact on the quality of thefinal product.

More specifically, by respecting the stoichiometric proportions and byadding an excess of DOTA intended not to be complexed with thelanthanide, it is not possible at the industrial scale to achievesufficiently reproducibly in the final pharmaceutical solution an excessof free DOTA in the target range, especially given:

-   -   1) the uncertainty of weighing at the industrial scale, which        does not make it possible to correctly ensure the ratio (of the        order of 1000) between the chelate and the excess chelate, given        the small amount of excess chelate;    -   2) the variability of the hygroscopic characteristics of the        chelate (associated with its acid functions).

It is pointed out, specifically, that to prepare an industrial amount,typically, for example 200 litres of a 0.5 M solution of gadoliniumchelate (for example DOTA-Gd), the amount of DOTA to be added in excessafter complexation of the DOTA with the lanthanide, to obtain an excessof free DOTA of 0.1 mol/mol %, would be about 40 g of DOTA in 200 litresof the DOTA solution (40 g in addition to the 40 kg of DOTA initiallyplaced in solution), which does not allow sufficiently reliablereproducibility at the industrial level.

This problem has been solved by the Applicant by means of using at leastone step of measuring in the liquid pharmaceutical formulationconcentrations of free macrocyclic chelate (C_(ch 1)) and/or of freelanthanide (C_(lan 1)) and at least one step of adjusting the C_(ch1)and/or the C_(lan 1) so as to obtain the desired concentration ofCa_(ch 1) and C_(lan 1)=0, advantageously by modifying the amounts ofmacrocyclic chelate or of lanthanide in the pharmaceutical composition.

C_(ch 1) abbreviation refers to the concentration of free chelate.

C_(lan 1) abbreviation refers to the concentration of free lanthanide.

Throughout the application, the equality C_(lan 1)=0 is used to definethat C_(lan 1) in the formulation injected into the patient is zero orsubstantially zero (typically less than 10⁻¹⁰ M and advantageously lessthan 10⁻¹² M or 10⁻¹⁴ M), the possible presence in solution of anextremely small amount of lanthanide not being able to be totallyexcluded. The reason for this is that concentrations less than 10⁻¹⁰ Mcannot be measured sufficiently reliably by the current analyticalmethods.

Thus, according to one aspect, the present invention relates to aprocess for preparing a liquid pharmaceutical formulation of complex ofmacrocyclic chelate with lanthanide, the said process comprising atleast one step of measuring in the liquid pharmaceutical formulationconcentrations of free macrocyclic chelate (C_(ch 1)) and/or of freelanthanide (C_(lan 1)) and at least one step of adjusting the C_(ch 1)and/or the C_(lan 1), so as to obtain (sufficiently stably in the finalpharmaceutical solution, i.e. the pharmaceutical formulation intended tobe administered to the patient) a mol/mol amount of free macrocyclicchelate of between 0.002% and 0.4%, advantageously between 0.02% and0.3% and very advantageously between 0.025% and 0.25%.

The present invention thus relates to a process for preparing a liquidpharmaceutical formulation containing a complex of macrocyclic chelatewith a lanthanide and a mol/mol amount of free macrocyclic chelate ofbetween 0.002% and 0.4%, advantageously between 0.02% and 0.3% and veryadvantageously between 0.025% and 0.25%, the macrocyclic chelateadvantageously being chosen from DOTA, NOTA, DOTAGA, DO3A, BT-DO3A(gadobutrol), HP-DO3A and PCTA, and is advantageously DOTA, the saidprocess comprising the following successive steps:

-   -   b) preparation of a liquid pharmaceutical composition        containing, firstly, the complex of macrocyclic chelate, with a        lanthanide, and, secondly, free macrocyclic chelate,        advantageously that is not under the form of an excipient        X[X′,L] in which L is the macrocyclic chelate and X and X′ are a        metal ion, in particular chosen independently from calcium,        sodium, zinc and magnesium, and/or free lanthanide;    -   c) measurement in the pharmaceutical formulation obtained in        step b) of the concentration of free macrocyclic chelate        C_(ch 1) and/or of free lanthanide C_(lan 1);    -   d) adjustment of C_(ch 1) and/or of C_(lan 1) so as to obtain        C_(ch 1)=C_(t ch 1) and C_(lan 1)=0, wherein C_(t ch 1) is the        target concentration of the free macrocyclic chelate in the        final liquid pharmaceutical formulation.    -   Advantageously, the process according to the present invention        comprises a prior step a) of determination of the theoretical        target concentration of free macrocyclic chelate C_(t ch 1) in        the final liquid pharmaceutical formulation.

The reaction is represented as follows as Scheme II (with “L” the ligandchelate, and “lan” the lanthanide gadolinium Gd3+ for example):

The reaction is in two steps:

Step 1:

[L]_(initial)+[lan]_(initial)-->[L-lan]_(initial)+[L]_(free) or[lan]_(free)

with the concentration C_(ch 1) of [L] and the concentration C_(lan 1)of [lan]_(free) being measured

Step 2:

[L-lan]_(initial)+[L]_(free) or [lan]_(free)+[L]_(adjustment) or[lan]_(adjustment)-->[L-lan]+[L]_(target free)

with the concentration C_(ch 1) ^(=C) _(t ch 1) of [L] _(target free)and C_(lan 1)=0 of [lan]_(free)

For the purposes of the present invention, the term “amount of freemacrocyclic chelate” means the proportion of free macrocyclic chelaterelative to the amount of complexed macrocyclic chelate (gadoteric acidin the case of DOTA-Gd) present in the formulation in mol/mol. In therest of the description, it will be referred to without preference asthe “amount of free macrocyclic chelate” or the “excess free macrocyclicchelate”. And as mentioned before, macrocyclic chelate L is not underthe form of an excipient X[X′,L] and is not complexed with any metal ion(namely X and X′).

For the purposes of the present invention, the term “free lanthanide”means any lanthanide not complexed with a macrocyclic chelate.

It is recalled herein that in document U.S. Pat. No. 5,876,695 for thelinear DTPA chelate, in Example 2, the amounts of excess chelate aredefined from the start on the calculated basis of the stoichiometry, andwithout a step of prior adjustment or measurement of the concentrations.More specifically, in the said example, 0.5 mol of DTPA and 0.25 mol ofgadolinium oxide (Gd₂O₃) are mixed in accordance with the stoichiometricproportions, and a 0.1 mol/mol % (0.5 mmol) excess of ligand is added;for macrocyclic chelates this does not ensure the target amount ofligand desired by the Applicant in the case of a large-scale industrialmanufacture.

It is precised that the use of an excess of free linear ligand DTPA isdestinated to scavenge free lanthanide that would otherwise be liberatedduring the conservation time of the formulation.

The adjustment process of the invention for macrocyclics isadvantageously destinated to make absolutely sure (in particular due tothe quantities used and to the detection limited capacities of theavailable analytical tools) that the level of free entities is totallycontrolled, and in particular that there is no free gadolinium in themanufactured pharmaceutical solution. This adjustment method isparticularly advantageous for the industrial complexation issued fromthe mixture of the chelate and the lanthanide in solution.

It is also reminded that, as know by the one skilled in the art, theprocess of adjustment of the Applicant would not be applicable at theindustrial scale with an excipient X[X′,L] in view of the thermodynamicand kinetic equilibrium of such excipient, except maybe if further verycomplex methods were used (the manufacturer would have to manage boththe metal ions and the lanthanide kinetic and thermodynamic constants).

As device for analysis/assay of the free macrocyclic chelate, anysuitable equipment is used. Advantageously, a potentiometer or capillaryelectrophoresis is used for the macrocyclic chelate. More specifically,in the presence of copper sulfate, the free DOTA contained in thesolution obtained from the complexation step (in bulk) complexes thecopper. The excess copper sulfate is assayed in preferably pH 5 bufferedmedium, by potentiometry, with a solution of EDTA in the presence of acopper-indicating electrode and a reference electrode.

The analysis/assay of the free lanthanide is performed by using, forexample, a solution of EDTA in the presence of xylenol orange Arsenezoas turning-point indicator. Free gadolinium is assayed advantageouslywith a colorimetric method using 0.01 M edetate disodium titrationsolution in the presence of xylenol orange as indicator. Titration iscarried out in pH=5 sodium acetate/acetic acid buffered solution on 20mL of DOTAREM product until the indicator turns colour from red toyellow. 0.1 ml of 0.01 M edetate disodium solution corresponds to0.0008% weight/volume of free Gd (8 ppm). The method is valid from 8 to100 ppm of free gadolinium

To the knowledge of the Applicant colorimetric methods are well knownbut it was neither known nor suggested to use them for the measure ofgadolinium Gd3+ in contrast agents at the very low levels of the presentinvention, which is of strong interest for the adjustment process of theinvention and belongs to the same inventive concept. As such theinvention also relates according to another aspect to an analyticalmethod of measuring free lanthanide at the low range of the applicationand consisting in a colorimetric method (also called potentiometricmethod).

The present invention concerns an analytical colorimetric method formeasuring the level of free lanthanide in a liquid pharmaceuticalformulation containing a complex of macrocyclic chelate with alanthanide and a mol/mol amount of free macrocyclic chelate of between0.002% and 0.4%.

In order to perform step d), several solutions are possible as afunction of the C_(lan 1) and C_(ch 1) measured in step c).

In particular, the following solutions are concerned:

-   -   if C_(lan 1)>0 and/or C_(ch 1)<C_(t ch 1), the adjustment may        advantageously be performed by adding free macrocyclic chelate        and/or by eliminating free lanthanide and/or by modifying the pH        as described herein below;    -   if C_(lan 1)=0 and C_(ch 1)>C_(t ch 1), the adjustment may        advantageously be performed by eliminating free macrocyclic        chelate and/or by adding free lanthanide and/or by modifying the        pH as described hereinbelow.

In the situation of an elimination of free lanthanide,[lan]_(adjustment) of Scheme 2 means that free lanthanide lan iseliminated.

In the situation of an elimination of free chelate, [L]_(adjustment) ofScheme 2 means that free chelate L is eliminated.

Advantageously, the elimination of free lanthanide is performed bypassing through an ion-exchange resin. It is thus possible, for example,to use a resin of styrene/divinylbenzene copolymers which containsiminodiacetate ions acting as chelating group for the binding with themetal ions (Gd³⁺ in particular).

Advantageously, the elimination of free macrocyclic chelate isperformed, for example, by filtration, advantageously using resins (forexample anionic resins).

In one particular embodiment, step b) consists in mixing a solution offree macrocyclic chelate (initial) and of free lanthanide (initial) soas to obtain complexation of the lanthanide by the macrocyclic chelate,advantageously by adding the lanthanide (preferably solid lanthanide)into the solution of free macrocyclic chelate. It is emphasized that theprior art did not suggest that the optimisation of the complexation (soas to reach the target quantity of free excess ligand) would require theadjustment method of the Applicant.

The lanthanide is advantageously added in the form of oxide (gadoliniumoxide in particular), but the invention also covers other possible formsof lanthanide, especially the lanthanide salts known to those skilled inthe art.

The precise experimental conditions of step b) are detailed in theexamples. Advantageously, the temperature for step b) is between 60 and100° C., and is advantageously about 80° C. Advantageously, thepharmaceutical formulation is then cooled before the adjustment step d).The duration of step b) is, for example, from 1 hour to 3 hours.

Moreover, throughout the description hereinabove and hereinbelow of theadjustment variants of step d), it is understood that the complexationstep b) may be performed in several sub-steps which would be equivalentto an overall complexation step. The complexation may be performed, forexample, by preparing about half the final volume of the tank, and thenadding gadolinium oxide at acidic pH.

It is possible to use a preparation process such that:

-   -   in step b), the amounts of free macrocyclic chelate (initial)        and of free lanthanide (initial) added are equal to the        stoichiometric proportions;    -   step c) consists in measuring C_(ch1) and/or C_(lan 1) ;    -   step d) consists in adding to the formulation obtained in        step b) the amount of free macrocyclic chelate necessary,        firstly, to complete, if necessary the complexation of the free        lanthanide and to obtain C_(lan 1)=0 (or substantially equal to        0), and, secondly, to obtain C_(ch 1)=C_(t ch 1).

For the purposes of the present invention, the expression “the amountsof free macrocyclic chelate and of free lanthanide added are equal tothe stoichiometric proportions” means that the amounts added are suchthat, in the light of the stoichiometry of the complexation reaction,all the lanthanide and all the chelate should be in complex form andthere should be no free macrocyclic chelate.

However, advantageously, it is preferred, in the process according tothe invention, for step c) of measurement of the concentrations to beperformed in a medium in which the complexation reaction of step b) isperformed:

-   -   by using a difference between the stoichiometric proportions and        the amounts of free lanthanide and of free macrocyclic chelate        added in step b),    -   or by modifying the pH to shift the chemical equilibria in        favour or in disfavour of complexation.

For the purposes of the present invention, the expression “differencebetween the stoichiometric proportions and the amounts of freelanthanide and of free macrocyclic chelate added in step b)” means thatthe amounts of free lanthanide and of free chelate added in step b) aresuch that, in the light of the stoichiometry of the complexationreaction, not all the lanthanide is complexed by the chelate (excesslanthanide and/or deficit of chelate relative to the stoichiometry) ornot all the chelate is complexed with the lanthanide (excess chelateand/or deficit of lanthanide).

Advantageously, this difference is such that the macrocyclicchelate/lanthanide or lanthanide/macrocyclic chelate mol/mol ratio isless than or equal to 1.4, advantageously between 1.001 and 1.3,particularly advantageously between 1.005 and 1.2, and in particularbetween 1.005 and 1.02. It is also pointed out that this ratio may beadapted depending on whether an excess of chelate or an excess oflanthanide is used. When an excess of lanthanide is used for thecomplexation, advantageously the lanthanide/macrocyclic chelate mol/molratio is typically less than or equal to 1.2. When an excess of chelateis used for the complexation, the macrocyclic chelate/lanthanide mol/molratio is advantageously less than or equal to 1.4.

Thus, in one advantageous embodiment, the amounts of free macrocyclicchelate and of free lanthanide added are such that not all themacrocyclic chelate is complexed with the lanthanide or such that notall the lanthanide is complexed with the macrocyclic chelate.Consequently, after this step b), the pharmaceutical formulation willtypically comprise macrocyclic chelate-lanthanide complex and:

-   -   either free macrocyclic chelate,    -   or free lanthanide.

In this case, the preparation process according to the present inventionis characterized in that, in step b), there is a difference between theamounts of free macrocyclic chelate and of free lanthanide added and thestoichiometric proportions, this difference advantageously being suchthat the macrocyclic chelate/lanthanide or lanthanide/macrocyclicchelate mol/mol ratio is less than or equal to 1.4, advantageouslybetween 1.001 and 1.3, particularly advantageously between 1.005 and 1.2and in particular between 1.005 and 1.02.

According to particular embodiments, the ratio will be, for example,1.01, 1.02, 1.03 or 1.04. This gives, for example, the concentrationspresented in Table 1 below, which shows the case of an excess of initialfree lanthanide, given that an excess of initial chelate may also beused.

Concentration of free Concentration of free macrocyclic chelatelanthanide (initial) (1) (initial) added in step b) added in step b)Lanthanide/chelate (M) (M) ratio 0.480 0.520 1.083 0.487 0.513 1.0530.492 0.508 1.032 0.497 0.504 1.014 (1) this is the amount of Gd³⁺, andnot of Gd₂O₃

For example, in the case of the chelate DOTA, an amount of free chelatecorresponding to a concentration of 0.497 M of chelate and an amount offree lanthanide corresponding to a concentration of 0.504 M oflanthanide, which corresponds to a lanthanide/DOTA mol/mol ratio ofx=1.014 (with x=0.504/0.497), will be added in step b).

Another way of expressing this difference relative to the stoichiometricproportions is to define it relative to the lanthanide concentration inthe final solution.

In the case of this example which illustrates an excess of lanthanide,the difference is 0.6%=100*[(0.5−0.497)/0.5)], for a formulation at 0.5M of gadolinium at stoichiometry. The difference is thus, for example,advantageously between 0.1 mol % and 2 mol % of the concentration atstoichiometry of the pharmaceutical formulation.

In one embodiment that is also advantageous (preferred mode) theadjustment step d) is performed without touching the total amount oflanthanide present in the formulation, i.e. without adding or removingany lanthanide. In this case, only the total amount of macrocyclicchelate and/or the pH is modified.

For the purposes of the present invention, the term “total amount oflanthanide” means all the lanthanide present in free form and incomplexed form.

For the purposes of the present invention, the term “total amount ofmacrocyclic chelate” means all the macrocyclic chelate present in freeform and in complexed form.

Thus, in a first case (case A of the preferred mode), an excess oflanthanide relative to the macrocyclic chelate is added in step b); andstep d) consists in adding free macrocyclic chelate.

In this case, the preparation process according to the present inventionis characterized in that:

-   -   in step b), the amounts of free macrocyclic chelate and of free        lanthanide added are such that not all the lanthanide is        complexed, the lanthanide/macrocyclic chelate ratio (mol/mol)        advantageously being less than 1.2;    -   step c) consists in solely measuring of C_(lan 1) , Ca_(ch 1)        typically being equal to 0 (or substantially equal to 0);    -   step d) consists in adding to the formulation obtained in        step b) the amount of free macrocyclic chelate necessary,        firstly, to complete the complexation of the free lanthanide so        as to obtain C_(lan 1)=0 and, secondly, to obtain an excess of        free macrocyclic chelate C_(ch1)=C_(t ch 1).

In a second case (case B of the preferred mode), an excess ofmacrocyclic chelate relative to the lanthanide is added in step b). Inthis case, depending on the excess of chelate, step d) consists inadding or removing macrocyclic chelate.

Specifically, when the excess chelate added in step b) makes it possibleto obtain C_(ch 1)<C_(t ch 1), it is then appropriate in step d) to addfurther free macrocyclic chelate in order to obtain C_(ch1)=C_(t ch 1).

On the other hand, if the excess chelate added in step b) makes itpossible to obtain C_(ch 1)>C_(t ch 1), it is then appropriate in stepd) to remove free macrocyclic chelate (where appropriate, to add freeGd) in order to obtain C_(ch1)=C_(t ch 1).

In this latter case, the preparation process according to the presentinvention is characterized in that:

-   -   in step b), the amounts of free macrocyclic chelate and free        lanthanide added are such that all the lanthanide is complexed        and that C_(ch 1)>C_(t ch 1), the macrocyclic chelate/lanthanide        ratio (mol/mol) advantageously being less than 1, 2;    -   step c) consists in solely measuring C_(ch 1), C_(lan 1) being        equal to 0;    -   step d) consists in removing the appropriate amount of free        macrocyclic chelate so as to obtain C_(ch 1)=C_(t ch 1).

It is pointed out that, in cases A) and B), as illustrated in thedetailed Example 2, the adjustment step d) comprises at the end a stepof adjustment of the pH and of the volume, advantageously with megluminefor DOTA.

In a third case (case C) the pH of the formulation (and optionally otherfunctionally equivalent chemical parameters) is controlled so as toshift the reaction equilibrium in order to obtain at the end the targetpharmaceutical solutions (excess amount of target ligand).

According to one embodiment, the preparation process is such that:

-   -   in step b), the amounts of free macrocyclic chelate and of free        lanthanide added are equal to the stoichiometric proportions;    -   it comprises between steps b) and c) an intermediate step b1) of        modifying the pH of the pharmaceutical formulation obtained in        step b) so as to shift the chemical equilibria in favour or in        disfavour of complexation;    -   step c) is performed on the formulation obtained in step b1);    -   step d) consists in adjusting C_(ch 1) and/or C_(lan 1) so as to        obtain C_(ch 1)=C_(t ch 1) and C_(lan 1)=0 (or substantially 0)        by modifying the pH so as to shift the equilibrium in the        direction opposite to that of step (b1) and optionally by adding        or removing free macrocyclic chelate.

For example, the process according to the invention is characterized inthat:

-   -   in step b), the mixing is performed at a pH of between 4 and 7,        advantageously between 5 and 6.5,    -   step b1) consists in increasing the pH using a base up to a        value of between 10 and 13 and advantageously between 11 and 12,    -   step d) consists in lowering the pH down to a value of between        6.5 and 7.5 and advantageously between 6.8 and 7.4, and        optionally adding or removing free macrocyclic chelate.

For example, the complexation is performed at a pH below 6 (for examplebetween 3 and 6 and advantageously between 5 and 6) and the pH is thenraised, for example, to about 12 (for example with NaOH), and the pH isthen adjusted to about 7.

In variants of the process without pH adjustment, as described in thedetailed Example 2 of the present patent application, in step 2, thecomplexation is typically performed at a pH below 6 (for example between3 and 6), the pH being brought directly to about 7. Without going intothe complex mechanisms, it is indicated that, given the thermodynamicconstants varying according to the pH, step b1) of the process with pHadjustment is such that it makes it possible to achieve the target rangeof excess free chelate in the pharmaceutical solution at least up to theexpiry of the shelf life of the pharmaceutical solution. Increasing thepH makes it possible to shift the equilibrium in the direction from anexcess of macrocyclic chelate to a level substantially equal to thetarget excess amount. Next, by reducing the pH, a reduction at a verylow rate in the amount of free macrocyclic chelate is obtained suchthat, over the shelf life of the product, the amount of freelanthanide/macrocyclic chelate does not change unfavourably. This wouldresult from the implied thermodynamic constants associated with the pHmodifications.

It may also be pointed out that when the free lanthanide measurementwill be performed (at pH 7), the concentration will be lower than if thepH change had not been made, and the adjustment is then made with thecorrect amount of chelate.

Furthermore, without going into the detail of the complexationmechanisms that take place at the molecular level in several phases(described especially in Chem. Eur. J., 2004, 10, 5218-5232), theApplicant points out that it was not at all obvious that the processwith adjustment would make it possible to obtain this result.

In another advantageous embodiment, step b) consists in preparing asolid complex [chelate-lanthanide] and in dissolving it (in water).

In this case, step d) is performed on a liquid formulation obtained bydissolving a solid [chelate-lanthanide] complex.

According to this embodiment, step b) of the process according to theinvention comprises two sub-steps:

-   -   i) the preparation of a solid complex [chelate-lanthanide] and    -   ii) the dissolution of the complex obtained in step i).

The adjustment in step d) may be performed as described previously indetail (addition of chelate or of lanthanide, removal of chelate or oflanthanide, adjustment by pH modification).

The preparation of the solid complex, which is advantageouslycrystalline [chelate-lanthanide], involves, where appropriate, at leastone treatment step (filtration, concentration, crystallization, drying,spraying, etc.) for obtaining the appropriate physicochemicalcharacteristics, especially in terms of solubility and purity.

As a conclusion, the manufacturing methods of the Applicant allow theoptimized control of the proper range of free ligand excess, which isimportant for the clinicians. In vivo the scavenging capacity towardsfree gadolinium is presumably much higher for free ligand (DOTA forinstance) than for excipient X[X′,L] (sodium salt of DOTA-Ca forinstance). Taking the example of DOTA as macrocyclic chelate,considering that the kinetic of complexation/uncomplexation of anexcipient X[X′,DOTA] is much less that of free DOTA, this excipientwould liberate the DOTA only slowly and/or a little in physiologicalsituation, as compared to the free DOTA. Thus free DOTA of theformulation of the applicant is, as regards to free Gd complexing,significantly more available than the DOTA of the excipient X[X′,DOTA],notably in case of an accumulation of complex in a biologicalcompartment. As a result, free DOTA excess is highly much better thanexcipient X[X′,DOTA] for avoiding the transmetallation due to freegadolinum in vivo.

It is precised that this is different from the case of linear chelates(DTPA-BMA notably), for which the excipient X[X′,L] is used because thisexcipient uncomplexes very quickly (or leads to quick transmetallation)and thus can scavenge free Gd. This effect of excipient X[X′,L] forlinear chelates has been recently demonstrated in vivo on human skin NSFpatients and this excipient is added in high quantity (5 to 10%mol/mol).

In addition, in another particularly advantageous embodiment, a furthertechnical problem was solved by the Applicant for the industrialmanufacture of a pharmaceutical formulation of contrast agent based on amacrocyclic chelate-lanthanide complex, while at the same time making itpossible to maximize the tolerance profile of the contrast product. Morespecifically, contrary to the prior-art teaching, for example U.S. Pat.No. 5,082,649 (excess of free calcium of 1 to 25%) which completes U.S.Pat. No. 5,876,695 (which uses large quantities of calcium chelate) inthe pharmaceutical formulation, the Applicant has demonstrated that, inthe case of the process according to the present invention, a very lowamount of calcium would make it possible to ensure the industrialcontrol of this process and to obtain a very well-tolerated product.

More specifically, the reliability of step c) of measuring the amountsof chelate and/or of lanthanide with common industrial analytical toolsis markedly improved when the amount of calcium in the components used(in particular in the macrocyclic chelate, the lanthanide and the waterused in step b)) is less than a very low target value of around 15 to200 ppm. The amount of calcium (quantity of calcium) in the macrocyclicchelate used in step b) is advantageously less than 200 ppm andadvantageously in the region of or less than 50 ppm and even preferablyless than 15 ppm. For example, if the amount of calcium in the DOTA[active principle in the form of powder supplemented with water in stepb)—see the detailed Example 2—dissolution step 1] is too high (andespecially greater than 200 ppm), calcium may complex the chelate andthe adjustment of the amount of free chelate will not be performedsufficiently satisfactorily.

The low amount of calcium in the pharmaceutical solution makes itpossible to avoid possible disadvantageous interferences regarding theassays of free macrocyclic chelate (for example by complexing thecalcium with the chelate) and thus to obtain an assay of the freechelate and its adjustment in a manner that is particularly effectivefor manufacture at the industrial scale at the required high level ofquality. Furthermore, a very low calcium concentration controlled in thefinal product administered to the patient (especially the meglumine saltof gadolinium DOTA) is advantageous as regards the calcaemia of thepatients in so far as it makes it possible to avoid any homeostasisimbalance: the impact of the injected product (typically at a dose ofless than 20 ml) on the calcaemia is at most in the region of 0.5%. Theamount of calcium in the administered contrast product is advantageouslyless than 50 ppm and especially less than 20 ppm, for example between 1and 5 ppm. For example, for the meglumine salt of gadolinium DOTA, alimit of 15 μg of Ca/g of DOTA powder (15 ppm) used in step b)corresponds to 3 μg Ca/ml of liquid contrast product administered to thepatient (there is about 0.202 g of DOTA per ml of administered liquidcontrast product), i.e. 3 ppm in this contrast product.

The different variants of the process according to the invention asdescribed previously thus advantageously comprise, before the measuringand adjustment steps c) and d), an intermediate step b2) of controllingthe amount of calcium in the formulations obtained in step b).

Where appropriate, in particular if the amount of calcium in the finalsolution is greater than 15 ppm or advantageously greater than 10 ppm,this intermediate step comprises, following this control, the removal ofthe excess calcium.

Thus, according to one aspect, the process according to the presentinvention is characterized in that the amount of calcium in the liquidpharmaceutical formulation administered to the patient is less than 50ppm, especially less than 20 ppm, and preferably less than 5 ppm, theprocess advantageously comprising, before step c), an intermediate stepb2) of measuring the amount of calcium and, where appropriate, ofremoving the excess calcium.

Furthermore, the different variants of the process according to theinvention as described previously advantageously comprise, before stepb), control of the amount of calcium in the components used in step b),and especially in the macrocyclic chelate intended to be dissolved, inthe lanthanide (typically used in oxide form), and in the water.Advantageously, the amount of calcium in these components is less than150 ppm and preferably less than 15 ppm. Thus, according to one aspect,the process according to the present invention is characterized in thatthe amount of calcium in these components (typically DOTA powder,gadolinium Gd2O3 powder, water) is less than 150 ppm and preferably lessthan 15 ppm. According to an aspect the invention concerns a DOTA as anintermediate product (DOTA powder or DOTA in aqueous solution)containing calcium at less than 150 ppm, preferably less than 50 ppm,and preferably less than 15 ppm.

Very advantageously, the Applicant has succeeded in removing the excesscalcium in the chelate (powder) used in step b), by means, in particularfor DOTA, of a purification by crystallization using a water-ethanolmixture, which makes it possible to obtain an amount of calciumadvantageously less than 50 ppm. The water used for step b) is alsoadvantageously purified, where appropriate by means of a suitabletreatment, for example descaling with acids to prevent any undesiredamount of calcium.

A gadolinium oxide with a purity very close to 100%, substantially of99.999%, will preferably be used in particular.

Furthermore, it will be preferred to check that the meglumine used atthe end of the adjustment step d) also comprises a small amount ofcalcium.

The process is also advantageously such that it uses components thathave extremely low amounts of metals (for example nickel and aluminium)liable to interact with the chelate, disrupting the assays. Thus, theprocess advantageously includes a step of checking the amount of thesemetals before the measuring and adjustment steps b) and/or c) and/or d).

Finally, the process according to the present invention alsoadvantageously comprises an additional step e) of checking C_(ch1) andC_(lan1), irrespective of the variant described above.

The process according to the present invention is, according to onepreferred embodiment, characterized in that the pharmaceuticalformulation is a pharmaceutical formulation of meglumine salt of theDOTA-gadolinium complex.

The Applicant's process makes it possible to obtain the targetformulations safely. This process makes it possible to solve the problemrepresented by the in situ complexation, in a pharmaceuticalmanufacturing reactor (into which is added the pharmaceuticalformulation agent). Specifically, when the lanthanide is Gd³⁺, megluminewill be used as formulation agent. However, given the physicochemicalcharacteristics of gadoteric acid, the mixing of the three components(powder of non-complexed chelate, lanthanide powder and megluminepowder) in the same reactor would not be sufficiently satisfactory.Thus, the process according to the invention that allows this problem tobe solved consists in engaging the complexation, measuring thedifference relative to the target, and adjusting.

Overall, the Applicant's process thus makes it possible to incorporatethe chelation process into the pharmaceutical production, with anadvantage especially in terms of cost price and quality.

In one advantageous embodiment, an agent for blocking the freelanthanide, other than the free macrocyclic chelate, is added in stepb). Advantageously, this blocking agent is a polycarboxylic acid,especially a dicarboxylic, tricarboxylic or tetracarboxylic acid, inparticular a citrate or a derivative thereof.

As regards the general inventive concept of the target range of amountof free macrocyclic chelate (0.002% to 0.4%, advantageously 0.02% to0.3% and in particular 0.025% to 0.25%), the Applicant points out thatthis range differs from the teaching of patent U.S. Pat. No. 5,876,695illustrated in particular by its examples, at least for the followingreasons.

The Applicant's target range is very narrow, and corresponds to aselection within the very broad range presented in the said document.

The formulations described in U.S. Pat. No. 5,876,695, which concernmacrocyclic chelates (especially Examples 3 and 4), are formulationswith salts of chelate (calcium disodium, zinc disodium DOTA) and notwith free chelate. The amounts of excess salts therein are moreover veryhigh, at least 10%. However, in the present patent application, only thefree chelates are used, and not in the faun of salts.

The formulations presented in U.S. Pat. No. 5,876,695, which have anamount of free chelate of about 0.1%, concern only linear chelates(DTPA), and the DTPA formulation at 0.08% described is clearly indicatedas a control solution, the said document suggesting, on the contrary,the use of a much higher amount, 2% or quite probably more.

Specifically, the only test presented as regards tolerance on the use ofchelates, in Table 2 and in column 6 (lines 62-67) of the said document,shows that the reduction in toxicity is markedly less favourable for anamount of linear free chelate of 0.08 mol/mol % (Formulation A for whichthe amount is established on the basis of the ratio between 0.5 mmol GdDTPA and 0.0004 mmol DTPA/kg), in comparison with the 2% amountcorresponding to the advantageous formulation (Formulation B for whichthe amount established on the basis of the ratio between 0.5 mmol GdDTPA and 0.01 mmol DTPA/kg) and which is described as a low value(column 6, line 61).

The Applicant thus worked on formulations with an amount of freemacrocyclic chelate about 5 to 100 times lower than that explicitlyrecommended by document U.S. Pat. No. 5,876,695. It was thusdemonstrated by the Applicant, surprisingly, that macrocyclic chelates,and more especially DOTA, behave differently from linear chelates suchas DTPA as regards tolerance, resulting from the presence of an excessof free chelate.

More specifically, whereas the tolerance appears to be improved withDTPA by increasing the excess free chelate from 0.08% to 2%, thetolerance degrades, in contrast, for DOTA by increasing the excess freechelate, passing from very low values (0.025% to 0.25%) to a value of2%. Consequently, the transposition of values to reduce the risk oftoxicity, between a linear chelate (in particular DTPA), and macrocyclicchelates (in particular DOTA), is not at all obvious. This is moreoverwhat is illustrated by the current complex discussions in the scientificcommunity in the context of NSFs with regard to the tens of millions ofdoses of contrast agents already injected in man, discussions on thesubject of the complexation kinetics and/or on comparisons of structuresbetween chelates. For instance it has recently been shown that in orderto reduce the risk of NSF (results on human skin where gadoliniumaccumulates) for some linear chelates, it is highly recommended to usevery high quantities of excipient X,X′L for linear chelates, namelyabout 5 to 10% of such excipient, and that free chelate such as DTPA-BMAshould clearly not be used.

To this end, according to another aspect, the invention relates to apharmaceutical formulation that may be obtained via the processaccording to the present invention, characterized in that it containsbetween 0.002 and 0.4 mol/mol %, more especially between 0.02 and 0.3mol/mol % and very advantageously between 0.025 and 0.25 mol/mol %, offree macrocyclic chelate, advantageously of free DOTA.

By virtue of the adopted selection of the range of excess freemacrocyclic chelate, in particular of free DOTA, a value of freelanthanide in solution, and in particular of gadolinium, of about from10⁻¹⁰ M to 10⁻¹⁴ M at physiological pH, is obtained.

The concentration of complexed chelate in the formulation is typicallybetween 1 μM and 1 M, with an administered dose of about from 0.01 to 5mmol/kg. The concentration of the injected formulation is typicallyabout 0.5 M.

The process particularly advantageously relates to the preparation ofthe pharmaceutical formulation of the meglumine salt of theDOTA-gadolinium complex: the macrocyclic chelate and the freemacrocyclic chelate are DOTA, the lanthanide is gadolinium, and theprepared salt is the meglumine salt.

Advantageously, the pharmaceutical formulation according to the presentinvention is characterized in that the macrocyclic chelate is DOTA andin that the formulation contains between 0.02 and 0.08 mol/mol % of freeDOTA.

This lower range is liable to have several physiological advantages:

-   -   limiting a risk of chelation for certain diseases of endogenous        cations (for example zinc or copper) by the presence of an        overly large excess of macrocyclic chelate,    -   limiting the inhibition of metalloenzymes, especially ACE, with        an impact on the regulation of arterial hypertension, for        example,    -   avoiding unfavourable medicinal interactions with metallic        active principles:

lithium, bismuth, platinum, etc.,

-   -   avoiding disrupting the seric dosages of endogenous metals,    -   avoiding medicinal interactions with active principles that are        complexing, for example detoxifying (deferroxamine, cyclam,        etc.).

In another advantageous embodiment, the pharmaceutical formulationaccording to the present invention is characterized in that themacrocyclic chelate is DOTA and in that the formulation contains between0.15 and 0.25 mol/mol % of an excess amount of free DOTA.

This higher range is liable to have several physiological advantages:

-   -   optimally limiting the amount of free gadolinium injected, the        free gadolinium being a toxicity risk and possibly being        involved in phagocytosis mechanisms associated with certain        diseases,    -   minimizing the in vivo transmetallation in pathological        situations, especially transmetallation by iron (increase in        seric iron).

This higher range is also an advantage for further improving thestability of the formulation to be injected over time (dechelation underunsuitable storage conditions: heat, depressurization in aircraft,excessive exposure to light, etc.).

According to one embodiment, the amount of free macrocyclic chelate isbetween 0.09% and 0.15%. This median range is liable to combineadvantages of the lower and higher ranges.

The choice of the amount of free macrocyclic chelate may be optimized inparticular as a function of the risk of the patients for variouspathologies or pathological risks associated with the mechanismspresented hereinabove. For example, in the case of patients presenting arisk of NSF, an excess of macrocyclic chelate in the median or highrange may be preferred, to minimize any release of gadolinium.

Very low values of excess free chelate are, however, also liable to havea beneficial effect in the pathology NSF if it turns out in certaincategories of patients (kidney failure patients in particular) that thispathology is partly associated with a presence of free chelate, whichwould involve in vivo transmetallation or similar phenomena that areunfavourable in terms of tolerance.

According to another aspect, the calcium content of the pharmaceuticalformulation (administered to the patient) according to the invention isless than 50 ppm, advantageously less than 30 ppm and advantageouslyless than 15 ppm.

According to another aspect, the invention relates to use of a contrastproduct formulation, the said formulation comprising a complex ofmacrocyclic chelate with a paramagnetic metal ion and an amount of freemacrocyclic chelate of between 0.025% and 0.25%, advantageously of aformulation according to the present invention, for improvement of thetolerance.

According to another aspect, the invention relates to a method forimproving the in vivo tolerance of an MRI contrast product based onmacrocyclic chelate, and more especially on DOTA, which consists inusing an excess of free chelate in an amount of between 0.025 and 0.25mol/mol %, especially 0.025-0.08%, 0.09-0.15%, 0.16-0.25%.

Advantageously, the concentration of chelate (complexed chelate) in theformulation is between 0.5 and 0.9 M.

The macrocyclic chelate that is useful in the context of the presentinvention is advantageously chosen from the following chelates: DOTA,NOTA, DO3A, BT-DO3A, HPDO3A, PCTA, DOTAGA and derivatives thereof; andis most particularly DOTA. The chemical formulae of these chelates arewidely known to those skilled in the art, and are recalled, for example,in WO 2007/042 504, on pages 20 to 23, and WO 2003/011115, on pages 8 to11.

The invention also relates to the use of a pharmaceutical formulationaccording to the invention for the preparation of a diagnosticcomposition for medical imaging, or for diagnostic monitoring of theefficacy of a therapeutic treatment, and to a diagnostic methodcomprising the administration of a pharmaceutically acceptable amount ofa formulation according to the invention.

For diagnosis in MRI, the intravenous administration by injectionusually as a saline solution is typically performed at a dose of from 1to 500 μmol Gd/kg. The pharmaceutically acceptable unit doses willdepend on the nature of the chelate, the route of administration, and onthe patient and especially on the nature of the disorder to be studied.For an intravenous injection and observation by magnetic resonance, theconcentration of the solution will typically be between 0.001 and 0.5mol/litre, and from 0.001 to 0.1 millimol/kg will be administered to thepatient, depending on the case. Higher clinical doses may also bepractised, for example a triple dose (0.3 millimol/kg). Theadministration rate, the concentration, the speed of injection areadapted according to the clinical indication and product specifications,and eventually also in view of the behavior of the contrast agent duringthe MRI procedure. Any appropriate protocol is used, with possibleadjustment of the administration in view of the patient data, of firsttest injections operated, of the enhancement curves obtained. The speedof injection may be calculated (advantageously automatically by datatreatment tools) according to the protocol and during the protocol inview of the relaxivity curve during the course of the acquisition; forinstance if the administration rate/speed is not sufficient for optimalenhancement considering the data base, the injector automaticallyincreases this rate during the MRI procedure.

Among the advantageous diagnostic indications, mention will be made ofthe indications already used clinically, and the indications for whichthe results are improved by virtue of the formulations according to theinvention. Mention will thus be made of the following indications andimprovements thereof: angiography, cerebral imaging, vascular imaging,imaging of cardiovascular, cancer, neurodegenerative and inflammatorypathologies, any indication with perfusion imaging, any indicationcombining the use of several contrast products, especially MRI, X-rayscanner, SPECT, PET, PET CT, and any indication with successiveadministrations of contrast products at the same or at differentconcentrations, or in multimodal imaging. According to embodiments,these novel formulations may be chosen to be administered in combinationwith or in place of prior-art formulations as a function of thediagnostic profile of the patient, and especially of the profile oftolerance of the patient to the contrast products. The choice may bemade by the practician and/or automatically by any tagging system (RFIDtag carried by the patient, . . . ) and conditioning the type ofadministration, for example the choice of the contrast agent bestadapted such as the formulation of the present application.

An installation comprising a device for evaluating the tolerance of thepatient, and a device like an injector for administering the formulationof the contrast product as a function of the result given by theevaluation device may thus be used. Several risks may be evaluated,especially the risk of NSF (nephrogenic fibrosis). Where appropriate,the MRI product is co-administered simultaneously with or subsequentlyto at least one anti-NSF therapeutic agent (anti-fibrosis agent knowntherapeutically, especially steroids, anti-inflammatories or vitamins,for example).

Where appropriate, an evaluation of the patient's risk with respect toNSF is performed to optimize the dose/concentration of injected contrastproduct (for example, the dose may be reduced relative to the commonclinical dose, if it makes it possible, while avoiding any risk, toobtain sufficiently satisfactory information to obtain the signal inimaging).

To further reduce the risk of toxicity of the lanthanide in the case ofat-risk patients, the Applicant also studied formulations comprising:

-   -   as in the prior art: the chelate of lanthanide (for example        gadoteric acid DOTA-Gd complex or a linear Gd-chelate) and the        salification agent for neutralizing the chelate, for example        meglumine (organic base),    -   but in addition with at least one biocompatible supplementary        excess blocking agent, intended to block any lanthanide (Gd³⁺)        that might otherwise remain free in the formulation.

Among the blocking agents that will especially be used are organicanions such as monocarboxylic or polycarboxylic acids (advantageouslytricarboxylic or tetracarboxylic, such as citrate and derivativesthereof), hydroxy acids (lactate, malate . . . ), or other agentscapable of an advantageous coordination interaction with the lanthanide.

The blocking agent may thus be introduced into the formulation and/orco-administered to the patient.

DETAILED EXAMPLES

1) Example 1: In Vivo Tolerance

The tolerance results in Table 2 (acute toxicity in mice for adiagnostic solution of DOTA; this solution is a pharmaceutical solutioninjected and comprising the complex of DOTA with the Gd3+, and an excessof free DOTA not complexed by Gd3+ and not complexed by metal ions asexcipient) show that formulations containing from 0.025 to 0.25 mot/mol% of free macrocyclic chelate DOTA are three times less toxic than theformulation close to 2%.

Excess of Free DOTA Male LD₅₀ Female LD₅₀ Test mol/mol % Mmol/kg Mmol/kg1 0.05 12.41 13.59 2 0.09 13.06 13.50 3 0.25 12.02 12.07 4 1.98 4.804.80

Further stability studies performed by the Applicant show that theformulations are very satisfying with no release of gadoninium for along conservation time.

Example 2: Process for Preparing Formulations of Lanthanide Chelate(Mixture of a Solution of Chelate and of a Solution of Lanthanide)

The preparation of formulations in which the macrocyclic chelate is DOTAis more specifically described. Table 3 below gives an example of theamounts used for the manufacture of a solution of 100 litres of DOTA(industrial amount).

Component Amount DOTA (1) 20.100 kg (i.e. 0.497M) Gadolinium oxide(expressed as 9.135 kg (i.e. 0.504M) anhydrous product) Meglumine(expressed as anhydrous 9.215 kg product) Solution for adjusting DOTA to5% qs 15-35 mg per 100 ml amount of free DOTA 3N meglumine solution qspH = 6.8-7.4 at 20° C. Injection-grade water qs 100 litres (1)1,4,7,10-Tetraazacyclododecane-N,N′,N″,N′″-tetraacetic acid

Step 1: dissolution

40 litres of injection-grade water at 80° C. are placed in a 100-litremanufacturing tank, the injection of nitrogen is started, and the 20.100kg of DOTA and the 9.135 kg of gadolinium oxide are then incorporatedwith stirring. The complexation is performed at a pH below 6, forexample between 3 and 6, for example at pH 4. The gadolinium oxide inthe presence of DOTA forms a water-soluble acid complex.

Step 2: measurements

After step 1, a sample is taken and the free gadolinium is assayed.

Step 3: adjustment of the free species

The adjustment of the solution is advantageously performed withgadolinium oxide or DOTA.

A DOTA-adjusting solution is thus added qs an amount of 15-35 mg per 100ml.

Step 4: cooling

The final solution from step 3 is cooled to 30° C., for example bycirculating cold water in the tank jacket.

Step 5: adjustment of the pH and of the mass per unit volume

The acid function of the complex formed is salified with meglumine andthe pH at 20° C. is adjusted to 6.8-7.4. The concentration is adjustedby adding injection-grade water.

The following are thus introduced into the manufacturing tank:

-   -   9.125 kg of meglumine    -   and a solution of meglumine pH=6.8-7.4 at 3N    -   injection-grade water, qs.

The final solution is then filtered and then placed in bottles typicallysterilized by autoclaving.

2) Example 3: Process for Preparing Formulations of Lanthanide Chelate(Dissolution of a Solid Complex [Chelate-Lanthanide])

This example illustrates the manufacture of a small amount of product,the appropriate transposition being performed at the industrial scale.

Int. 1 Int. 2 (Gd₂O₃) Int. 3 M_(w) (g · mol⁻¹) 404.42 362.70 580.63 m(g) 10 4.48 n (mol) 0.025 (1 Eq) 0.0125 (0.5 Eq)

10 g (0.025 mol; 1 eq) of macrocyclic chelate DOTA are dissolved in 200ml of water by heating to 80° C., in a three-necked flask equipped witha condenser, a thermometer and a pH meter. The measured pH is 3.7. It isadjusted to 6 with 2N NaOH solution. 4.48 g (0.0125 mol; 0.5 eq) ofgadolinium oxide are added. The pH is readjusted and kept stable atbetween 6 and 7 by adding 1N HCl. The reaction is left at 80° C. withstirring.

The residual free gadolinium is removed by means of a chelex resinprerinsed with water. To do this, the reaction mixture is brought to pH5 (the resin is more efficient). The whole is left for 2 hours withstirring at room temperature. The pH rises to between 6.5 and 7. Theresin is removed by filtration.

The complex is precipitated in ethanol to remove the salts (5 volumes ofEtOH per 1 volume of water).

An assay of the salts is performed by titration with a 0.05N silvernitrate solution.

Quantification of the free gadolinium is also performed by colorimetricassay with Arsenazo (III). 11.5 g of product are obtained (whitepowder). Yield=80%; HPLC purity: 98%; LC/MS (ES⁴ mode): z=1 (m/z=559).

The dissolution in water is then performed via suitable methods, forexample using a water at 45° C., with stirring for about 30 minutes, andwith adjustment of the pH.

The invention covers broadly other embodiments deriving from the onespresented in detail. For instance the meglumine is added to a solutionof DOTA and afterwards gadolinium is added for the step of DOTAcomplexation by gadolinium.

1-37. (canceled)
 38. Industrial process for preparing a liquidpharmaceutical formulation containing a complex of macrocyclic chelatewith a lanthanide and a mol/mol amount of free macrocyclic chelate ofbetween 0.002% and 0.4%, said process comprising the followingsuccessive steps: b) preparing a liquid pharmaceutical formulationcontaining a complex of macrocyclic chelate with a lanthanide, and: freemacrocyclic chelate, and/or free lanthanide; said step b) consisting inthe preparation of a solid complex [chelate-lanthanide] and in thedissolution of the said complex in water; c) measuring, in a sample ofthe liquid pharmaceutical formulation obtained in step (b), C_(ch 1),the concentration of free macrocyclic chelate C_(ch 1) and/or of freelanthanide C_(lan 1); d) adjusting C_(ch 1) and/or C_(lan 1) in theliquid pharmaceutical formulation by adding to the liquid pharmaceuticalformulation obtained in step b): if C_(lan 1)>0 and/orC_(ch 1)<C_(t ch 1), free macrocyclic chelate, if C_(lan 1)=0 andC_(ch 1)>C_(t ch 1), free lanthanide, so as to obtainC_(ch 1)=C_(t ch 1) and C_(lan 1)=0, with C_(t ch 1) representing thetarget concentration of the free macrocyclic chelate in the final liquidpharmaceutical formulation, C_(t ch 1) being selected in the range ofbetween 0.002% and 0.4% mol/mol; wherein the amount of free macrocyclicchelate in the final liquid pharmaceutical formulation corresponds tothe proportion of free macrocyclic chelate relative to the amount ofcomplexed macrocyclic chelate DOTA-Gd in the final liquid pharmaceuticalformulation in mol/mol, wherein the macrocyclic chelate is DOTA and thelanthanide is gadolinium, and wherein the operating steps b) and d) ofthe process occur in the same reactor.
 39. The process of claim 38,wherein the mol/mol amount of free macrocyclic chelate of between 0.025%and 0.25%.
 40. The process of claim 38, wherein the liquidpharmaceutical formulation is a liquid pharmaceutical formulation of themeglumine salt of a DOTA-gadolinium complex.
 41. The process of claim40, wherein the adjustment step (d) comprises at the end a step ofadjustment of the pH and of the volume.
 42. The process of claim 41,wherein the pH is adjusted with meglumine.
 43. The process of claim 38,wherein step (b) is carried out at a temperature of between 60° C. and100° C.
 44. The process of claim 38, wherein step (b) is carried out at80° C.
 45. The process of claim 38, wherein the preparation of the saidsolid complex involves at least one treatment step chosen fromfiltration, concentration, crystallization, drying and spraying, forobtaining the appropriate physicochemical characteristics in terms ofsolubility and purity.
 46. The process of claim 38, wherein any calciumpresent in the final liquid pharmaceutical formulation is present in anamount of less than 50 ppm.
 47. The process of claim 46, wherein theamount of calcium present in the final liquid pharmaceutical formulationis less than 20 ppm.
 48. The process of claim 47, wherein the amount ofcalcium present in the final liquid pharmaceutical formulation is lessthan 5 ppm.
 49. The process of claim 46, wherein the liquidpharmaceutical formulation is prepared from ingredients includingchelate powder, water and meglumine, and wherein the amount of calciumin the ingredients used to prepare the final liquid pharmaceuticalformulation is less than 50 ppm.
 50. The process of claim 46, wherein itcomprises, before step (c), an intermediate step (b2) of measuring theamount of calcium in the obtained solution, and removing any excesscalcium in order to obtain an amount of less than 50 ppm in saidsolution.
 51. The process of claim 38, wherein it comprises anadditional step (e) of checking C_(ch 1) and C_(lan 1).
 52. The processof claim 38, wherein step (b) is carried out at a temperature of between60° C. and 100° C. and in that the liquid pharmaceutical formulation isthen cooled before the adjustment step (d).
 53. The process of claim 38,wherein gadolinium is added as gadolinium oxide in step (b), and whereappropriate in step (d).
 54. The process of claim 38, wherein the liquidpharmaceutical formulation is an injectable solution.
 55. The process ofclaim 38, wherein step (c) is carried out at pH 7.